Fernando Alonso goes into the Belgian Grand Prix not with the best chance to win but it is Jenson Button who won the pole position. For Button to win the title he'll need to basically beat Alonso every race for the rest of the season. The RedBulls are strong but it is expected they might not finish the season as strong considering their GP wins came early in the season when they had a design advantage that was later rejected by FIA for them to fix.
During this time Alonso has only got faster and become more consistent of a driver. Perhaps Lewis Hamilton is the only driver that can really catch him but this could even be too late for him.
The fastest pit stops of the season belong to McLaren and Ferrari. At least Ferrari are the fastest on average because they don't bundle anything the way McLaren's have done all season. If McLaren cars have their act together maybe they can team up to make a push for either a world drivers championship title and also to challenge for the world constructors championship.
The odds for all of these don't look great but if you think that RBR are on the downturn and McLaren's can only go up, this looks like an easy decision to make and money in the bank for making any sort of bet like this.
Regardless of what happens for the rest of the season, the title is still up for grabs and should remain so late until the last race of the season. It will probably take until the Brazilian grand prix race to determine who wins both championship titles.